Method of positioning a magnetic head

ABSTRACT

An apparatus for positioning at least one magnetic head relative to a magnetic tape for recording and reproducing information includes a head unit for holding at least one magnetic head and a moving unit for moving the head unit parallel to a surface of the magnetic tape in a direction along the width of the magnetic tape so that the head unit is kept at a constant angle relative to the surface of the magnetic tape.

This is a divisional application of copending U.S. patent applicationSer. No, 08/278,938 filed Jul. 22, 1994, now pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a magnetic tape memorydevice, and particularly relates to a method of and an apparatus forpositioning a magnetic head relative to a magnetic tape in a directionalong the width of the magnetic tape in a magnetic tape memory devicewhich has a rotary head.

2. Description of the Prior Art

In computers, for example, the magnetic tape is used as an additionallarge volume memory media or as a backup memory media for copyinginformation stored in memory devices such as hard-discs. A magnetic tapeis wrapped around a pair of tape reels which is contained in a datacartridge, and a torque roller for rotating the pair of reels isprovided on the front face of the data cartridge. When the datacartridge is inserted into a magnetic tape memory device, the magnetictape memory device rotates the pair of reels by conveying torque throughthe torque roller. The magnetic tape is driven just inside the frontface of the data cartridge, and the recording or reproducing ofinformation is carried out by a magnetic head which is positioned so asto touch the magnetic tape.

Regarding such a memory device, there are methods in which a rotary headis used instead of a fixed conventional head in order to increase thememory volume, and one of these methods is a semi-circle scanningmethod.

FIGS. 1A and 1B show the semi-circle scanning method. As shown inFIG.1A, the recording and reproducing of information is carried out byrotating a rotary head 12 with magnetic heads 12b mounted on theperimeter of a head holder 12a and by driving a magnetic tape 11 in adirection A. In recording and reproducing information, the magneticheads 12b touch the surface of the magnetic tape 11.

Since the magnetic heads 12b revolve around the center of the headholder 12a, record tracks 11a formed on the surface of the magnetic tape11 have a shape of an arc. Thus, when reproducing information, thepositioning of the rotary head 12 relative to the magnetic tape 11 hasto be precise in order to obtain a correctly reproduced signal. To thisend, the position of the rotary head 12 relative to the direction alongthe width of the magnetic tape 11 is strictly controlled by using aservo method.

A servo method requires appropriate data as a basis for control. Thisdata is provided as servo data P, Q, and R as shown in FIG. 1B, wherethe servo data Q and R are recorded near the edges of the magnetic tape11, and the servo data P is recorded at the center. The servo data P, Q,and R are recorded such that the distance between P and Q and thedistance between P and R are the same. When reproducing information, therotary head 12 is controlled to be positioned in a manner whichsatisfies the two conditions described below. First, the time distancebetween two signals reproduced from the servo data P and Q is the sameas the time distance between two signals from the servo data P and R.Second, the address numbers of the servo data P, Q, and R are all thesame. Here, the address numbers of the servo data P, Q, and R arerecorded at the time of recording information, and are all made equalwithin one track.

FIGS. 2A and 2B show a schematic illustration of a rotary head unit 10.In the rotary head unit 10 of FIG. 2A, the magnetic heads 12b areprovided on the perimeter of the head holder 12a, which is rotated by ahead motor 13. The head motor 13 is mounted on a supporting base 14.

Tape guides 15a and 15b which position the magnetic tape 11 are providedon both sides of the head holder 12a. Supporting plates 16a and 16b (notshown) are provided on the sides of the supporting base 14 atapproximately the center thereof. The supporting base 14 can rotateabout rods 17a and 17b (not shown) in a direction B-C (a direction alongthe width of the magnetic tape 11). Also, the supporting base 14 isprovided near the back end thereof with a voice coil unit 18 to controlthe movement of the supporting base 14 in the direction B-C.

The positioning of rotary head 12 relative to the magnetic tape 11 iscarried out by controlling electric current provided for the voice coilunit 18 on the basis of the signals reproduced from the servo data P, Q,and R.

However, since the rotary head 12 is rotated around the rods 17a and 17bwhen its relative position to the magnetic tape 11 is being controlled,movement of the rotary head 12 in the direction B-C draws a shape of anarc as shown in FIG. 2B. Thus, the angle of the rotary head 12 relativeto the surface of the magnetic tape 11 varies according to the positionof the rotary head 12. This means that a reproduced signal has aproclivity to become unstable, which in turn means that the positioningof the rotary head 12 is also unstable.

Accordingly, there is a need in the field of magnetic tape memorydevices for a method of, and an apparatus for, positioning a rotary headrelative to a magnetic tape while keeping a constant angle between therotary head and the surface of the magnetic tape.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea method and an apparatus which satisfies the need described above.

It is another and more specific object of the present invention toprovide an apparatus for positioning a rotary head relative to amagnetic tape while keeping a constant angle between the rotary head andthe surface of the magnetic tape.

In order to achieve this object, according to the present invention, anapparatus for positioning at least one magnetic head relative to amagnetic tape for recording and reproducing information includes a headunit for holding at least one magnetic head and a moving unit for movingthe head unit parallel to a surface of the magnetic tape in a directionalong the width of the magnetic tape so that the head unit is kept at aconstant angle relative the surface of the magnetic tape.

In a preferred embodiment of the present invention, the apparatusfurther includes a supporting unit for enabling the head unit to pivoton an axis perpendicular to the surface of the magnetic tape. Thus, thehead unit can move in a direction along the width of the magnetic tapewhile being kept at a constant angle relative to the surface of themagnetic tape.

It is yet another object of the present invention to provide a method ofpositioning a rotary head relative to a magnetic tape.

In order to achieve this object, according to the present invention, amethod of positioning at least one magnetic head relative to a magnetictape for recording and reproducing information, which at least onemagnetic head circles around an axis perpendicular to the magnetic tape,includes the steps of reproducing signals by the at least one magnetichead from a reference magnetic tape, each of the signals being recordedin a longitudinal line at a different transverse position of thereference magnetic tape, positioning the axis relative to the referencemagnetic tape in a predetermined transverse position of the referencemagnetic tape by using the signals, creating reference data regardingthe predetermined transverse position, and secondly positioning the axisrelative to the magnetic tape by using the reference data. Since thepositioning of the axis is based on the reference data created by usingthe reference magnetic tape, the positioning of the axis can be highlyprecise, variations in magnetic tape cartridges or magnetic tape memorydevices due to manufacturing variations can be compensated for, and thetime required for positioning the axis can be reduced by a significantamount.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are illustrative drawings showing a rotary head alongwith a magnetic tape and servo data recorded on the magnetic tape,respectively;

FIGS. 2A and 2B are a perspective view and a side view of a rotary headunit, respectively;

FIG. 3 is a perspective view of a head positioning unit according to thepresent invention;

FIGS. 4A and 4B are a perspective view of a head base of FIG. 3 and aside view of a rotary head of FIG. 3, respectively;

FIGS. 5A and 5B are illustrative drawings showing reference tracksrecorded on a magnetic tape and magnetization of a track, respectively;

FIG. 6 is a flow chart of a procedure for positioning the rotary headrelative to a reference magnetic tape according to the presentinvention;

FIGS. 7A and 7B are illustrative drawings showing reproduced signalscorresponding to the reference tracks and showing an index signal,respectively;

FIG. 8 shows a relation between time difference t1 minus t2 anddeviation of the rotation center of the rotary head from the center ofthe magnetic tape; and

FIG. 9 is a flow chart of a procedure for positioning the rotary headrelative to a magnetic tape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 shows a perspective view of a head positioning unit according toa preferred embodiment of the present invention. A head positioning unit21 shown in FIG. 3, which is provided in a magnetic tape memory device,comprises a rotary head 22 and a head base 23. The head base 23comprises a head holder 24, a holder base 25, and a stepping motor 26.

The rotary head 22 is provided with magnetic heads 32 mounted on arotating part 31 at equal intervals. The rotating part 31 is rotated bya driving motor 33.

FIG. 4A is a perspective view of the head base 23, whose structure willbe described with reference to FIGS. 3 and 4A. The head base 23 in FIG.4A is shown from the direction opposite to that of FIG. 3.

In FIGS. 3 and 4A, the head holder 24 of the head base 23 is used forcontaining the driving motor 33, and has a cylindrical shape. The headholder 24 has on one side a protruding part 24a, which is in contactwith a link 38, and has on the opposite side hinge parts 24b1 and 24b2,which are connected to the holder base 25.

The holder base 25 serves as a base for mounting the head holder 24, andis mounted on a frame base of the magnetic tape memory device. A rod 34connects the head holder 24 and the holder base 25 together, and aspring 35 pushes down the head holder 24, so that the protruding part24a is pushed against the link 38. The rod 34 extends in a directionperpendicular to the surface of the magnetic tape.

The link 38 is mounted on the holder base 25 by a rod 38a, has one endin contact with the protruding part 24a, and has the opposite end fixedto a nut 36. A lead screw 37, which is rotated by a stepping motor 26,is fitted into the nut 36. With the head holder 24 being pushed againstone end of the link 38, the stepping motor 26 can control the positionof the head holder 24 by rotating the lead screw 37 to move the nut 36and the opposite end of the link 38 up and down. Since the link 38rotates around the rod 38a, the head holder 24 is moved up when the nut36 is moved down, and the head holder 24 is moved down when the nut 36is moved up. In this movement, the head holder 24 pivots on the rod 34.

The stepping motor 26 is driven according to servo signals which will bedescribed later.

FIG. 4B shows the movement of the rotary head 22. As noted above, thehead holder 24 of FIG. 4A pivots on the rod 34, so that the rotary head22 moves in a direction parallel to the surface of a magnetic tape 41.Thus, the angle of the rotary head 22 relative to the surface of themagnetic tape 41 does not vary as the rotary head 22 moves.

With reference to FIG. 3 again, tape guides 39a and 39b are provided forpositioning the magnetic tape relative to the rotary head 22. Also, astopper 40 is integrally formed with the tape guide 39b, and serves as aunit for positioning a cartridge containing a magnetic tape.

The driving motor 33 of FIG. 3 provides an index signal to indicate acertain position of the rotary head 22 with regard to its rotationalangle. That is, when the rotary head 22 rotates to come into apredetermined position once in 360 degrees, the driving motor 33rotating the rotary head 22 outputs an index signal. This index signalis used for determining the position of the rotary head 22. The use ofthe index signal will be described later.

FIGS. 5A and 5B show control data recorded on a reference magnetic tape42, and FIG. 6 shows a flow chart for generating reference data by usingthe reference magnetic tape 42, which data is used for positioning therotary head 22 relative to the magnetic tape 41.

As can be inferred from the above, there are two different phasesinvolved in the positioning of the rotary head 22 relative to themagnetic tape 41. First, reference data is obtained by using thereference magnetic tape 42 prior to recording and reproducinginformation on the magnetic tape 41. Second, the rotary head 22 ispositioned relative to the magnetic tape 41 by using the reference dataobtained for this positioning.

In FIG. 5A, a reference center track 51 is formed in the center of thereference magnetic tape 42, and signal tracks 52 and 53 are formed atequal distances from the reference center track 51. In these tracks 51,52, and 53, remnant magnetic domains are formed in opposing directionsas shown in FIG. 5B.

In FIG. 6, at a step S1, the reference magnetic tape 42 is inserted intothe magnetic tape memory device. Upon this insertion, a reproducingoperation starts according to a reproducing procedure of the device,and, at a step S2, a reproduced signal is obtained. As shown in FIG. 7A,the reproduced signal has three signal outputs 61, 62, and 63 appearingin a time sequence, which correspond to the tracks 51, 52, and 53,respectively. Here, the time length between signal outputs 61 and 62 isreferred to as t1, and the time length between signal outputs 61 and 63as t2.

At a step S3, t1 and t2 are compared with one another. If t1 is equal tot2, it is determined that the current position is the center of therotation of the rotary head 22, and a step S5 is the next step toproceed. If t1 is not equal to t2, the procedure returns to the step S2after adjusting the position of the rotary head 22 at a step S4. Then,the steps S2, S3, and S4 are repeated until t1 and t2 become equal.

FIG. 8 shows an illustration of the relation between the time differencet1 minus t2 and the deviation of the rotation center from the center ofthe reference magnetic tape 42. Here, it is assumed that the diameter ofa magnetic head revolution is 7.62 mm, the distance between thereference center track 51 and each of the signal tracks 52 and 53 is 2mm, and the rotation rate of the rotary head 22 is 7500 rpm. As shown inFIG. 8, when the rotation center is deviated by 1 μm from the center ofthe reference magnetic tape 42, the time difference t1 minus t2 is about0.35 μsec. By using the relation shown in FIG. 8, the position of therotary head 22 is adjusted at the step S4.

At the step S5, the number of pulses P applied to the stepping motor 26in order to move the rotary head 22 from the possible lowest position tothe current position is stored in a memory.

As noted above, the driving motor 33 generates an index signal, as shownin FIG. 7B, to indicate a predetermined position of the rotary head 22with regard to its rotational angle. At a step S6, the time length Tbetween this index signal and the signal output 61 corresponding to thereference center track 51 is stored in a memory.

Based on the number of pulses P and the time length T, the positioningof the rotary head 22 relative to a magnetic tape 41 is controlled asdescribed below.

The following are the reasons for having to prepare the reference data.First, with the help of the reference data collected before therecording and reproducing of information on the magnetic tape 41, thepositioning of the rotary head 22 relative to the magnetic tape 41 canbe realized by using a single reference signal, which is onlyprerecorded at the BOT (Beginning Of Tape) of the magnetic tape 41 shownin FIG. 1B. Second, this positioning method can reduce by a significantamount the time needed to position the rotary head 22, compared to thecase where three reference signals are used, even if such signals areprerecorded at the beginning of the magnetic tape 41.

FIG. 9 shows a flow chart of a procedure for positioning the rotary head22 relative to a magnetic tape 41.

At a step S1, the magnetic tape 41, which has a reference signalprerecorded at the BOT as shown in FIG. 1B, is inserted into themagnetic tape memory device. After the insertion of the magnetic tape41, the rotary head 22 is moved up by the number of pulses P at a stepS2 so that the rotary head 22 is positioned at approximately the centerof the magnetic tape 41. Then, the reference signal prerecorded at theBOT of the magnetic tape 41 is reproduced at a step S3.

At a step S4, the time length Ts between the index signal and the signaloutput 61 corresponding to the reference signal is measured. At a stepS5, the time length Ts is compared with the time length T.

If Ts is equal to T, this is the end of the process. If Ts is greaterthan T, the rotary head 22 is moved down, and if Ts is smaller than T,the rotary head 22 is moved up. This adjustment of the position of therotary head 22 is carried out at a step S6. Then, the steps S3, S4, S5,and S6 are repeated until Ts becomes equal to T. When Ts becomes equalto T, the rotary head 22 is positioned precisely in the center of themagnetic tape 41.

As described above, in positioning the rotary head 22 relative to themagnetic tape 41, the number of pulses P is used for initiallypositioning the rotary head 22 at approximately the center of themagnetic tape 41. Thus, a significant amount of time is saved, whichtime would otherwise have to be used for positioning the rotary head 22at approximately the center of the tape by starting from an arbitraryinitial position, which might be far away from the center.

In the head positioning unit according to the preferred embodiment ofthe present invention, a rotary magnetic head can be moved while beingkept at a constant angle relative to the surface of the magnetic tape,so that stable reproduced signals can be obtained. Also, since thepositioning of the rotary head relative to the magnetic tape is based onthe reference data recorded on the magnetic tape, variations in theposition of the magnetic tape inside the cartridge or the position ofthe rotary head inside the device due to manufacturing variations can becompensated for. Furthermore, the positioning of the rotary head iscontrolled by means of a stepping motor, which lowers the cost formanufacturing the device.

Further, the present invention is not limited to this embodiment, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

What is claimed is:
 1. A method of positioning at least one magnetichead relative to an information recording/reproducing magnetic tape,said positioning being carried out in a direction parallel to the widthof the recording/reproducing magnetic tape and transverse to the lengthof said tape, the recording/reproducing magnetic tape having a surfaceapplied to the magnetic head, said at least one magnetic head rotatingabout an axis perpendicular to the surface of the recording/reproducingmagnetic tape, said method comprising the steps of:reproducing aplurality of signals from said at least one magnetic head obtained froma reference magnetic tape, one of said signals being recorded from alongitudinal line located at a center transverse position of saidreference magnetic tape, others of said signals being recorded fromother longitudinal lines spaced at predetermined equal intervals fromsaid center transverse position transversely across said referencemagnetic tape; moving the at least one magnetic head to position saidaxis relative to said reference magnetic tape in a predeterminedtransverse position of said reference magnetic tape by using saidsignals and so that time intervals between said one of reproducedsignals and said other reproduced signals are equal so that saidpredetermined transverse position is said center transverse position ofsaid reference magnetic tape, and so that said one reproduced signaloccupies a center timing position between the timing of said otherreproduced signals; creating reference data regarding said predeterminedtransverse position comprising a first time length between an indexsignal and the reproduction of said one reproduced signal provided whensaid axis is in said center transverse position, and storing saidreference data obtained from said reference tape in a memory; andthereafter reproducing a signal from said at least one magnetic headobtained from the recording/reproducing magnetic tape, said signal beingrecorded from a center longitudinal line of said recording/reproducingmagnetic tape; and moving the at least one magnetic head to positionsaid axis relative to the recording/reproducing magnetic tape by usingsaid reference data obtained from said reference tape and stored in saidmemory, the movement being carried out until a second time lengthbetween said index signal and said signal recorded from said centerlongitudinal line of said recording/reproducing magnetic tape equalssaid first time length, thereby to position said at least one magnetichead relative to said recording/reproducing magnetic tape.
 2. The methodas claimed in claim 1, wherein said plurality of signals comprise threesignals, one of said three signals being recorded from said longitudinalline in said center transverse position of said reference magnetic tape,the other two of said three signals being recorded from longitudinallines parallel to said longitudinal line and at equal time intervalsfrom said center transverse position.